Assessment of three-dimensional physical-biological ECOHAM1 simulations byquantified validation for the North Sea with ICES and ERSEM data

The Ecological North Sea Model, Hamburg Version 1 (ECOHAM1) simulates phosp horus-related phytoplankton processes in relation to the physical dynamics of the North Sea. This three-dimensional model calculates annual primary pr oduction, the main related processes in the North Sea and regional variatio ns on a 20 km(2) basis, kand at 5 m vertical resolution. The simulation for 1985 was driven by the actual physical forcing that occurred, and took int o account monthly river loads from 14 rivers, the daily velocities and diff usivities from a baroclinic North Sea model, and solar radiation calculated every 30 min. The high level of variability of the forcing generates consi derable variability in physical and biological dynamics. The simulated chlo rophyll and phosphate concentrations were validated by a cost function, nor malized in units of standard deviation of data. The validation with ICES da ta indicates how well the model performs over a coarse time and spatial sca le of 1 degrees x 0.5 degrees boxes with long-term seasonal averages. The p hosphate cost functions for the three seasons are: 1.03 in winter, between 1.51 and 1.99 in spring, and between 1.85 and 1.9 in summer. Horizontal dis tributions of the cost function for phosphate and chlorophyll are presented . An additional validation step is the evaluation of annual cycles in speci fic locations of the ERSEM boxes of 1 degrees x 1 degrees. The ERSEM data c onsists of climatological monthly means. The annual cycle for a box in the German Eight shows a cost-function value of 2.21, and for the Dutch coast a value of 1.27. The main difficulty of the model is calculating correctly t he winter and early spring chlorophyll concentrations. (C) 2000 Internation al Council for the Exploration of the Sea.